1. Field of the Invention
The present invention relates to a magnetic random access memory (MRAM) using a magneto-resistive effect element as a storage element.
2. Description of the Related Art
In recent years, research and development of a magnetic random access memory which stores data in a non-volatile manner by utilizing a magneto-resistive effect have been frequently carried out. One of characteristics of the magnetic random access memory lies in that realization of a finer element and higher integration is possible.
However, when realization of the finer element and higher integration advances, irregularities in the operation characteristic of an internal circuit caused due to shifting of a pattern or irregularities in an element shape in manufacture become large.
Therefore, in the magnetic random access memory, the operation characteristic of the internal circuit is inspected, and irregularities in the operation characteristic are confirmed. Thereafter, based on the irregularities, conditions for reducing the irregularities in the operation characteristic of the internal circuit, i.e., tuning information is programmed in an information storage portion in a chip.
It is to be noted that the tuning information is read from an information storage portion when turning the power supply and operation conditions of the internal circuit, e.g., a value of an internal power supply potential (DC potential), a value of write current, a value of a reference current in a sense amplifier, a sense timing or the like are determined based on the tuning information.
In the conventional magnetic random access memory, trimming information for adjusting the operation characteristic of the internal circuit, redundancy information for substituting a defective cell by a redundant cell, ID information of the magnetic random access memory and others are programmed in a fuse element.
As a method for programming the information in the fuse element, there are a method for cutting the fuse element by using a laser and a method for electrically disconnecting the fuse by an excessive current or an excessive voltage (E-FUSE).
In case of the method for cutting the fuse element by using the laser, since the fuse can not be cut after packaging, the tuning information must be of course programmed in the fuse element in the wafer state before packaging. Therefore, this method can perform only adjustment of the internal circuit by which the operation characteristic test can be conducted.
In case of the method for disconnecting the fuse element by using an excessive current, the fuse element is blown out by giving the excessive current to the fuse element from an external element of the package. Further, in case of the method using an excessive voltage, dielectric breakdown is caused by giving an excessive voltage to the fuse element from the external element of the package, thereby storing the information in the fuse element.
However, in case of programming the information in the fuse element, which includes the method for electrically disconnecting the fuse element by using the excessive current or the excessive voltage, when the information is once programmed in the fuse element, there is a problem that re-programming is impossible.
Meanwhile, in the magnetic random access memory, the memory cell stores data in the non-volatile manner, and data in the memory cell can be electrically rewritten many times. Therefore, the tuning information can be programmed in a part of the memory cells in the memory cell array.
In this case, however, a write/read circuit for writing/reading data must be usually utilized in order to write/read the tuning information. Thus, the write/read circuit itself must be designed/manufactured in such a manner that it can constantly correctly operate irrespective of the turning information.
In other words, as to the characteristic of the write/read circuit, since adjustment can not be carried out based on the tuning information, there may occur a possibility that the tuning information which must be correctly read may not be correctly read.